Small Craft Advisory 281, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 AM AKDT Fri Mar 27 2020

.ANALYSIS AND UPPER LEVELS...

A fairly well defined upper trough and surface front over the
eastern Bering Sea is spreading snow across Southwest Alaska and a
mixture of rain and snow along the Alaska Peninsula. The cloud
shield associated with the frontal boundary is spreading high
clouds over Southcentral under which high pressure with cooler
temperatures inland and weak low pressure over the Gulf is
producing dry offshore flow. Gusty outflow conditions with
this synoptic setup across Southcentral is also producing
brisk outflow/gap winds along the Gulf coast and
favored inland areas.

&&

.MODEL DISCUSSION...
Models are in fair agreement through the next few days. The most
notable differences are track and strength of a series of short-
waves crossing the southern Alaska mainland today through
Saturday. Handling of these waves has also been inconsistent
between model runs. This makes sense, as models tend to struggle
with multiple short-waves in fast flow aloft. While there is high
confidence in the forecast for widespread snow across Southwest
and Southcentral Alaska the next couple days, the differences
noted created high uncertainty in total snow accumulation for any
specific location or region. Thus, expect to continue to fine-tune
snow amounts over the next 24 hours.

&&

.AVIATION...
PANC...Generally light winds should prevail. Snow developing early
this evening will bring the potential for MVFR to IFR conditions.
Ceilings and visibilities will improve Saturday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Gusty outflow and gap winds across Southcentral will diminish
through this morning/early afternoon hours. A weak front boundary,
which has slowed from previous model runs, brings a mixture of rain
and snow to Kodiak Island this morning and not much in the way of
snow to the Southcentral mainland until this afternoon/evening hours.
Snow accumulations overall are expected to be light across Southcentral
as the flow aloft remains generally out of the west and the brunt
of the energy travels south with a wave that develops along the
frontal boundary. That said, expect some lingering snow to hold
into Saturday until the upper trough finally drives south into the
Gulf. This will signal and end to precipitation and a return
to broad offshore flow with locally brisk outflow/Gap winds Saturday
night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

An active pattern returns for Southwest Alaska as a front
continues to move inland this morning. As the front continues to
progress eastward towards the Kuskokwim Valley and Bristol Bay,
it begins to fall apart, but not before bringing a few inches of
snowfall across the region throughout the day. A second front
quickly moves in behind this first one for the Kuskokwim Delta
this afternoon, allowing for a second round of snow.

A Winter Weather Advisory remains in effect for the Kuskokwim
Delta through Saturday morning, which will see higher snowfall
totals (4 to 6 inches, localized areas up to 8 inches) from this
long duration snowfall event. In addition to the snow, strong
westerly onshore flow near the Kuskokwim Delta Coast to Bethel
will will bring reduced visibility in blowing snow conditions,
with lowest visibilities to one half mile occurring Saturday
morning.

Temperatures will be on a downward trend through the weekend as
cold air advection continues to moves in to the Kuskokwim Delta
on Saturday. The cold air will keep spreading into the rest of
Southwest Alaska, with low temperatures dropping back into the
single digits through the end of the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Active weather remains over the eastern Aleutians and Bering this
morning as a front moves inland over Southwest Alaska by this
afternoon. The associated low near St. Lawrence Island will
continue its track inland overnight tonight, keeping a showery
pattern for the eastern Aleutians and AKPEN through Saturday. By
Saturday afternoon, a low approaches the central Aleutians,
bringing a brief period of precipitation.

With cold air advection moving in behind this low, heavy freezing
spray, along with gale force winds, will return to the eastern
Bering overnight tonight through Saturday night.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska...

Gale force gap winds are likely to continue into Sunday morning
south of Kodiak Island, out of the Barren Islands, and out of the
Copper River Delta. The winds will diminish Sunday afternoon,
with no gales expected from Sunday night through Tuesday. Freezing
spray may be common in windy areas with colder air moving into
the region.

Bering Sea...

There is high confidence that gale force winds will impact the
waters west of St. Matthew Island on Sunday. The winds will
diminish Sunday night. Gales are possible to the west of a low
that will track near the central Aleutians Tuesday. This is low
confidence however as there remains significant uncertainty with
the track and strength of the low. Heavy freezing spray and gale
force winds through the gaps south of the Alaska Peninsula are
likely to persist from Saturday night through the day Sunday.
Rapidly diminishing winds are expected late in the day Sunday,
ending this threat.

&&

.LONG TERM (Days 3 through 7: Sunday through Thursday)...

The long term forecast begins with good model agreement through
Sunday and Monday, followed by a loss of agreement and significant
uncertainty through the end of the week. The good news is that for
Sunday and Monday, there is good agreement that the weather will
be quiet across southern mainland Alaska. There is also good
agreement that we are in for a pair of much colder than normal
days as well. Cold air that moves in behind the low on Saturday
will dig in across the area on Sunday. This will keep gap winds
strong, especially across Southcentral, including around Kodiak
Island, the Copper Delta, Seward, and the Valdez marine areas.
Freezing spray, potentially heavy at times will be possible across
many of those same marine areas. As the low moves off and the high
to the west both weaken through the day on Sunday, all the winds
will diminish on Monday.

By Tuesday, the model agreement rapidly diminish regarding how
they handle a front over the Bering and a low over the Gulf, the
EC wants to keep both features stronger, lifting them moisture and
threaten coastal communities in both Southwest and Southcentral
with precipitation. Meanwhile the GFS is dry as the Bering front
dissipates and the low over the Gulf remains much further south.
Model agreement only diminishes further for Wednesday and beyond.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155.
MARINE...Gale 132 165 180 181 185 352 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...JW